Conventionally, as valves for use under high-pressure or high-temperature environments, for example, trunnion-type ball valves have been known. In this valve, normally, a seat as a valve seat is attached to a valve body, and this seat is provided so as to be resiliently pressed and pushed onto the ball valve body by a resilient force of a spring attached to a gap of the body via a retainer gland, thereby allowing sealing by the seat on the upstream side against a fluid.
In this case, to improve sealability between the seat and the valve body, a packing material is attached therebetween. As a packing for high-pressure and high-temperature use, one made of expanded graphite is generally used. Unlike a rubber-made packing, this expanded-graphite-made packing material has a so-called non-self-sealing characteristic, which exerts sealability by being continuously given a pressing force. Thus, when the expanded-graphite-made packing material is used, a stepped packing insertion part is provided on a seat outer peripheral side, and the expanded-graphite-made packing material formed to have a rectangularly-shape in cross section is attached to this packing insertion part as being compressed and in a close contact state. With this packing material being pressed by the resilient force of the spring and the fluid pressure, sealability is retained.
As a ball valve of this type, a ball valve of PTL 1 is disclosed. In this ball valve, an annular ball seat is retained in an annular seat retainer, and an expanded-graphite-made packing material is attached in a close contact state between a gap provided between this seat retainer and a gland resiliently pressed by a spring.
Furthermore, in FIG. 5 of the literature, a tapered part is formed on a packing insertion part of the seat retainer to more improve a surface pressure force of the packing material. After the valve is assembled, the packing material is pressed by the resilient force of the spring and the fluid pressure to an insertion direction of the packing insertion part via the retainer gland, and is pressed to a sealing direction, that is, an outer periphery portion, by the packing insertion part provided by a tapered part to have a wedge shape.
On the other hand, in a ball valve of PTL 2, a sealing packing material is inserted between a valve body and a ring-shaped seat, and a wedge-shaped tapered part is formed on a depth side of the packing material of the ring-shaped seat, and a metal-made seal ring is inserted between this tapered part and the valve body and the packing material via a backup plate. The packing material is elastically deformed so as to increase its diameter to inner and outer diameter directions by pressure of an entering fluid and a pressing force by an elastic restoring force of a disc spring to seal between the ring-shaped seat and the valve body.